1. Field of the Invention
The present invention relates to a retrofocus type wide angle lens and, more particularly, to a wide angle lens which has a total field angle of about 75.degree., and has an aperture ratio as bright as about 1:2.8.
2. Related Background Art
Some conventional retrofocus type wide angle lenses are made compact using a small number of lenses. As a wide angle lens of this type, lenses disclosed in, e.g., U.S. Pat. Nos. 4,008,952 and 4,221,467, and Japanese Laid-Open Patent Application No. 56-22406 are known.
However, a wide angle lens disclosed in U.S. Pat. No. 4,008,952 has a back focus as short as about 1.07 times its focal length, and is not practical as a lens for a single-lens reflex camera. Furthermore, the wide angle lens disclosed in U.S. Pat. No. 4,008,952 has a total field angle as narrow as 64.degree., and an aperture ratio as dark as 1:3.5.
Although wide angle lenses disclosed in U.S. Pat. No. 4,221,467 and Japanese Laid-Open Patent Application No. 56-22406 are made compact, since coma is substantial at the upper and lower peripheral portions of the frame, these wide angle lenses have poor imaging performance at these portions, and cannot be put into practical applications.